welp, I guess we got the answer, Sensei isn't a lolicon!.. well, at least old timeline sensei. Who knows what Chise's tampering has done to his psyche.
But damn, 2 huge twists at once. The less signifigant but interesting one is that onee-san now knows the whole plot-line. Doesn't change too much but I guess she's now even more ship crazy to throw her 11 year old little sister into her teacher. RIP, kinda liked having a not illegal girl lusting after sensei, but I guess she did say she'll back off a few chapter back (i.e. she wants to join in lol. You don't just sneak in a kiss if you want to back off lol). (the next block is just a plot summary)
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But boy, we now get the full story of the old timeline Sensei. Definitely not what I was expecting out of what was just some loli harem romcom. Nanami gets into her choice of middle school and competes as a dancer. But then she has an injury which gets her put out of the running and has her spiraling down into depression Who put Blue Reflection into my Uran manga?. Eventually leading to her running away from home, getting shelter from random men, and eventually getting pregnant from one of those men. She was 6 months pregnant after Sensei found her and took her in. So not only is Sensei single in 6-7 years, he may not even still be a virgin. Truly the twist of twists.
But it only gets darker from there. Nanami took advantadge of that kindness and Sensei took her in, married her, and took care of the child as his own for some 3-4 years, becoming a full time caretaker so that assumedly Nanami could get her life back. A soul for a soul. Given what we see of sensei it makes perfect sense that he cares so much for his students, current or past. And I guess he felt guilt because his intervention toppled the dominoe that lesd to this.
At some point something, for reasons we still don't fully know (and proabbly won't ever know, since Chise told the story) happened. Maybe he couldn't handle the strain of the life he lost, maybe he thought this last act would help out Nanami dead more than he could do while alive, maybe it was a freak accident. But Sensei's life more or less ends via carbon monoxide poisoning putting him into a permanent comatose state.
And despite hearing all that, it seems he chooses to walk his path. He will still choose to do what's right even knowing it leads to his own death. Truly a teacher.
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I guess the obvious fault here (and Chise's blame) is Nanami. As Chise says, she self destructed and ultimately dragged Sensei down with her. Outside of recommending a middle school, all these events would happen years after Nanami would leave Sensei so it makes sense to blame her. So Chise's plan is silly but I guess makes sense. Kill two birds with one stone: have her forget Nanami and furfill her lifelong crush that she traveled 12 years back in time for.
Title aside, I guess we see why she chose 5th grade. She said long ago that she time jumped back once, waited until she was 18 (so, 8 years from the current setting) and would proceed to confess. But by then it was too late. As we now know, this would be 2 years after Sensei took in and married Nanami, and 2 more years before he kills himself. Legal adult was too late to stop the spiral down. So she went further and decided to seduce him early lol.
HOWEVER, when you really think about it the final boss is... nanami's mom. It's not clear from Chise's POV because she didn't meet her parents in the old timeline, but it's pretty clear from sensei's experiences. Even if he stops Nanami from breaking her leg it'll be something else down the line. Maybe a boy, maybe some dance routing the mom thinks it too sexy, etc. But without intervening, Nanami will probably end up running. All because the mom is ashamed of her own past and is pushing her daughter way too far to avoid something that probably wouldn't ever happen to begin with if she had a normal childhood.
There's time to fix this, but not a whole ton. 3 years before Nanami breaks her leg, maybe another year before she runs away. I just wonder if Sensei or Chise will realize this first.